Field of the Invention
The invention relates to a changeover device which uses both analog and digital signals as input signals and supplies an analog output signal.
Such a changeover device can be used wherever an analog output signal has to be available for further processing and the analog output signal can be obtained both from a digital input signal and from an analog input signal.
In television technology, analog and digital signals are often processed at the same time. The video signal which is broadcast by the television stations for the purpose of television picture transmission, is converted into the baseband in a television receiver and is present as a color, video, blanking, syncs signal (CVBS), has an analog nature. If the picture information of the CVBS signal is intended to be processed further, it is frequently converted into a digital video signal in order to utilize the advantages of digital signal processing. Picture-in-picture insertions constitute an example of this. The analog picture information of an additional picture which is intended to be inserted into a main picture as a picture that is reduced in size is processed after analog-to-digital conversion. The processing of the digital video signal may serve for example for matching the format of the additional picture to the main picture. After processing, the digital video signal is converted back into an analog video signal, from which RGB signals are generated which can be fed to a picture tube.
The amplitude of the RGB signals should be independent of whether they are obtained directly from an analog signal or from an analog signal after analog-to-digital conversion and subsequent digital-to-analog conversion.